A guide gib or holding device for valve tappets or cam followers is used in valve operating mechanisms of internal combustion engines as an assembly, rotation-preventing and orientation means. So-called plastic lifter guides are already known, in which, however, the required alignment torques necessitate large contact faces of the flattened portions. To increase functional reliability, the connections of the valve tappets to the lifter guides are usually designed as press fits. Considerable frictional forces therefore occur during operation. In certain embodiments of guide gibs, said frictional forces require the spring forces of the valve tappets to be increased to a high level. Said increase is however opposed by the small available installation spaces of the tappets. On the other hand, certain minimum sizes of the contact faces are necessary for the functional reliability of such a guide gib. One significant advantage of said solution is the possibility of freely shaping the plastic, for example by means of an injection-moulding process. In addition, the “soft” plastic permits significant distortion as a result of production-related positional tolerances, without causing large forces and stresses within the component and in the contacting regions.
The document DE 102 12 522 A1 also mentions that, in internal combustion engines, it is known to prevent a roller tappet from rotating by using a plastic bridge, in which the tappet is held by a real guidance. Here, at least one planar face section is formed on the casing of the cylindrical tappet, said planar face section interacting with a corresponding planar surface section of a holding space of the holding device. To simplify transport and assembly of the valve operating mechanism parts, the tappets are pre-assembled on the holding device with contact pressure at the mutually contacting faces.
The document U.S. Pat. No. 5,088,455 A presents a holding device in which the necessary clamping of the tappet for assembly also remains effective during later engine operation, when only the rotation-preventing function is required. Said document describes an assembly aid or holding device which is injection-moulded from plastic with corresponding glass fibre reinforcement. Said assembly aid or holding device is however only designed for standard roller tappets, that is to say the positioning and the correct location of the tappet are of secondary importance here.
The document DE 197 12 610 A1 explains that internal combustion engines conventionally have roller tappets which engage with cam lobes of a camshaft. Since the tappets cannot rotate about their longitudinal axis because the rollers on the tappets must remain in the same plane as the cam lobes, the tappets are suitably aligned in the cylinder block of the internal combustion engine using holding devices, said tappets being prevented from rotating.
So-called metal lifter guides are also already known, in which, however, positional tolerances and production tolerances have an unfavourable effect because of the greater stiffness in relation to plastic. In addition, a solution in which there is rotational play can also give rise to functional concerns; the greater the play, the greater the negative functional influences. A significant advantage of said solution is the high degree of security against wear of the active faces. With current heat treatment processes, it is possible in such metal components to obtain surface strengths which permit high contact stresses. This facilitates, in conjunction with the high modulus of elasticity of the material of the guide gib, “play guides” for preventing rotation, with simultaneously small active faces.
A guide gib of the type mentioned in the introduction is known from DE 101 63 411 A1. Said guide gib can consist entirely either of a plastic or of a metallic material.